On 3/9/2011 12:10 PM, Darren New wrote:
> Invisible wrote:
>> The point is *totally* to have a PK that never changes,
>
> Well, yes, that's the desire. But you can only achieve that by having
> meaningless PKs on everything, which I find to be undesirable if a
> meaningful PK can be found.
>
> If your database is likely to be big enough that an incorrect initial PK
> is going to be catastrophic, then you can go for meaningless PKs.
>
> However, in Tom's case, the GPS coordinates being wrong means
> *everything* is wrong for that pole, so changing the GPS coordinates
> might as well be treated as deleting the pole in the wrong place and
> creating the pole in the right place.
>

Not exactly - we at times have to 'adjust' the coords to achieve better 
accuracy once they are int he system.  It sucks that after you get a lot 
of data your client gives you the 'revised' requirements that cause such 
changes.

>> OK, well I'm gonna have to say they must be doing something more
>> precise than "stand in the general vicinity of the intersection, take
>> down the GPS coordinates, and we'll just use those".
>
> I don't know.
>

look at aerial imagery - see pole - that's the GPS.  Better than 
anything else we have.  GPS units are too slow to get good numbers that 
close.


>
> There's a certain level of error of a couple of meters. You pick a
> standard place to measure from (such as the center of the manhole that
> you're interested in) and call that your location.
>
> When you go back to find the intersection, are the GPS coordinates given
> good enough that someone else can tell what intersection you're talking
> about?
>
> It should be noted, btw, that they're not really interested in the
> intersections, but in the wires running under the roads. The same PK can
> be used to track the wires running under or over not-roads as well.
>

We have had clients require specs that someone in an office without 
experience must have come up with.  Must be withing xx accuracy - must 
add up to +- xx difference.  Possible, but very expensive to actually 
meet the requirements.

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